This invention relates generally to the control of an etch line and particularly to such control utilizing the multi-measurement of the energy transmission capability of apertures etched in a sheet of material.
In the manufacture of shadow masks for color television kinescopes, a roll of flat material is coated with a photoresist material and is subsequently photo exposed to form a series of aperture patterns and the peripheries of the shadow masks on the photoresist material. The unexposed photoresist material is then washed away leaving the bare material. The bare material is then subjected to an acid etching process in which the bare material is removed to form the apertures and partially etched peripheries used to remove the shadow masks from the strip of material. After the etching is completed, the transmission of actinic energy, typically light, through the apertures is measured to verify that the shadow masks are suitable for the intended use. The result of the measurement typically is used to control one, or more, of the etching process parameters to optimize the energy transmission capability of the etched apertures. It is undesirable to make the energy transmission measurement immediately following the etching of the apertures because the material is still wet with the etching or rinsing solutions which inhibit the transmission of energy and render the measurement inaccurate. It is equally undesirable to measure the light transmission capabilities after the etched shadow masks are completely rinsed and dried because improper etching is detected at a later time and a large number of masks are improperly etched before the measurement is made.
The instant invention overcomes these disadvantages by the provision of a control system which utilizes an early energy transmission measurement immediately after the first rinse cycle and a second energy transmission measurement after the apertures are fully dried. The results of the two measurements are combined into a predicted transmission signal which is used to control at least one of the etch line control parameters.